366 EMBRYOLOGY 



and at last mounted in pure glycerin acidified with formic acid. 

 We arc inclined to believe that the Champy-Kull or Regaud 

 fixation (the latter with a post-osmication) would be much 

 superior to the above method, that is, for sectioning. 



Many authors have used picro-nitric, picro-sulphuric, picro- 

 fomiol with or without corrosive, chromic-acetic acid, Flemming 

 and Hermann, and so on, but one cannot help thinking that the 

 more modern and logical fixation methods will be better. This 

 seems borne out by the late work of Lams {Arch, de Biol., t., xxiii), 

 and Levi (Arch.f. Zellf., xiv.) 



J. P. Hill (Quart. Journ. Micr. Soc, 1910) gives the formula of 

 a " Marsupial mixture " for fixation of ova and blastocysts of 

 Marsupials. This fluid is made by adding to 96 c.c. of Mayer's 

 picro-nitric, 2 c.c. of 1 per cent. OsO^. Two c.c. of glacial acetic 

 acid may be added, but the picric acid is sufficiently penetrative 

 without the addition of acetic acid. 



J. A. Long (Contrib. Zool. Lab. Museum Contpar. Zool. Harvard, 1912) 

 describes an ingenious constant temperature box for working with fresh 

 egg of mammalia. A circulation shde is also described in detail. So far 

 J. A. Long has succeeded in keeping mice eggs alive and under observa- 

 tion for only twelve hours. 



J. A. Long and E. L. Mark (op. cit.) use a modified Zenker for their 

 study on mouse eggs. They fix for from twenty to sixty minutes in a 

 mixture of (A) 4 per cent, bichromate of potash. (B) 4 per cent. (aq. sol. ) 

 sublimate and 20 per cent, acetic acid. For use, mix equal portions of A 

 and B. Wash out in warm water for twelve to fourteen hours, 70 per cent, 

 alcohol and iodine twelve to fourteen hours, quickly dehydrate, clear 

 in xylol and imbed in paraffin. Mark and Long's fixative appears to 

 us (on paper at least) to be far too acid. It may be indicated for 

 chromosome work. 



804. Subsequent Treatment of Ova. After fixation the eggs or 

 blastocysts should be brought into 30 per cent, alcohol and slowly 

 U2:)graded to 90 per cent, alcohol : at this stage they may be stuck 

 on pieces of liver or brain by Minchin's albumen method ; the 

 egg is placed on the liver and albumen is gentty pipetted over it. 

 The alcohol coagulates the albumen, and enables the object to be 

 handled more easily. Another method used by J. P. Hill (Quart. 

 Journ. Micr. Science, 1910) is to bring the ova into alcohol absolute 

 and then into equal parts of alcohol absolute and ether. Then 

 take a hand-cut section of liver or brain (which has been stored in 

 absolute) place 1 drop of 0-5 per cent, solution of photoxylin (or 

 celloidin) in equal parts of absolute alcohol and ether ; then 

 transfer the egg on a flat camel hair brush to this drop, and harden 

 the object in 15 per cent, chloroform in 90 per cent, alcohol. 

 Transfer to equal parts of absolute alcohol, xylol and chloroform. 

 Then equal parts of chloroform and xylol, and imbed in paraffin 

 wax. 



The process of sticking the eggs to the hard cut liver or hrain section 

 should he carried out under a dissecting microscope. 



